import {
	NotEqualDepth,
	GreaterDepth,
	GreaterEqualDepth,
	EqualDepth,
	LessEqualDepth,
	LessDepth,
	AlwaysDepth,
	NeverDepth,
	CullFaceFront,
	CullFaceBack,
	CullFaceNone,
	DoubleSide,
	BackSide,
	CustomBlending,
	MultiplyBlending,
	SubtractiveBlending,
	AdditiveBlending,
	NoBlending,
	NormalBlending,
	AddEquation,
	SubtractEquation,
	ReverseSubtractEquation,
	MinEquation,
	MaxEquation,
	ZeroFactor,
	OneFactor,
	SrcColorFactor,
	SrcAlphaFactor,
	SrcAlphaSaturateFactor,
	DstColorFactor,
	DstAlphaFactor,
	OneMinusSrcColorFactor,
	OneMinusSrcAlphaFactor,
	OneMinusDstColorFactor,
	OneMinusDstAlphaFactor,
} from '../../constants.js';
import { Vector4 } from '../../math/Vector4.js';

function WebGLState(gl, extensions, capabilities) {
	const isWebGL2 = capabilities.isWebGL2;

	function ColorBuffer() {
		let locked = false;

		const color = new Vector4();
		let currentColorMask = null;
		const currentColorClear = new Vector4(0, 0, 0, 0);

		return {
			setMask: function (colorMask) {
				if (currentColorMask !== colorMask && !locked) {
					gl.colorMask(colorMask, colorMask, colorMask, colorMask);
					currentColorMask = colorMask;
				}
			},

			setLocked: function (lock) {
				locked = lock;
			},

			setClear: function (r, g, b, a, premultipliedAlpha) {
				if (premultipliedAlpha === true) {
					r *= a;
					g *= a;
					b *= a;
				}

				color.set(r, g, b, a);

				if (currentColorClear.equals(color) === false) {
					gl.clearColor(r, g, b, a);
					currentColorClear.copy(color);
				}
			},

			reset: function () {
				locked = false;

				currentColorMask = null;
				currentColorClear.set(-1, 0, 0, 0); // set to invalid state
			},
		};
	}

	function DepthBuffer() {
		let locked = false;

		let currentDepthMask = null;
		let currentDepthFunc = null;
		let currentDepthClear = null;

		return {
			setTest: function (depthTest) {
				if (depthTest) {
					enable(gl.DEPTH_TEST);
				} else {
					disable(gl.DEPTH_TEST);
				}
			},

			setMask: function (depthMask) {
				if (currentDepthMask !== depthMask && !locked) {
					gl.depthMask(depthMask);
					currentDepthMask = depthMask;
				}
			},

			setFunc: function (depthFunc) {
				if (currentDepthFunc !== depthFunc) {
					if (depthFunc) {
						switch (depthFunc) {
							case NeverDepth:
								gl.depthFunc(gl.NEVER);
								break;

							case AlwaysDepth:
								gl.depthFunc(gl.ALWAYS);
								break;

							case LessDepth:
								gl.depthFunc(gl.LESS);
								break;

							case LessEqualDepth:
								gl.depthFunc(gl.LEQUAL);
								break;

							case EqualDepth:
								gl.depthFunc(gl.EQUAL);
								break;

							case GreaterEqualDepth:
								gl.depthFunc(gl.GEQUAL);
								break;

							case GreaterDepth:
								gl.depthFunc(gl.GREATER);
								break;

							case NotEqualDepth:
								gl.depthFunc(gl.NOTEQUAL);
								break;

							default:
								gl.depthFunc(gl.LEQUAL);
						}
					} else {
						gl.depthFunc(gl.LEQUAL);
					}

					currentDepthFunc = depthFunc;
				}
			},

			setLocked: function (lock) {
				locked = lock;
			},

			setClear: function (depth) {
				if (currentDepthClear !== depth) {
					gl.clearDepth(depth);
					currentDepthClear = depth;
				}
			},

			reset: function () {
				locked = false;

				currentDepthMask = null;
				currentDepthFunc = null;
				currentDepthClear = null;
			},
		};
	}

	function StencilBuffer() {
		let locked = false;

		let currentStencilMask = null;
		let currentStencilFunc = null;
		let currentStencilRef = null;
		let currentStencilFuncMask = null;
		let currentStencilFail = null;
		let currentStencilZFail = null;
		let currentStencilZPass = null;
		let currentStencilClear = null;

		return {
			setTest: function (stencilTest) {
				if (!locked) {
					if (stencilTest) {
						enable(gl.STENCIL_TEST);
					} else {
						disable(gl.STENCIL_TEST);
					}
				}
			},

			setMask: function (stencilMask) {
				if (currentStencilMask !== stencilMask && !locked) {
					gl.stencilMask(stencilMask);
					currentStencilMask = stencilMask;
				}
			},

			setFunc: function (stencilFunc, stencilRef, stencilMask) {
				if (currentStencilFunc !== stencilFunc || currentStencilRef !== stencilRef || currentStencilFuncMask !== stencilMask) {
					gl.stencilFunc(stencilFunc, stencilRef, stencilMask);

					currentStencilFunc = stencilFunc;
					currentStencilRef = stencilRef;
					currentStencilFuncMask = stencilMask;
				}
			},

			setOp: function (stencilFail, stencilZFail, stencilZPass) {
				if (currentStencilFail !== stencilFail || currentStencilZFail !== stencilZFail || currentStencilZPass !== stencilZPass) {
					gl.stencilOp(stencilFail, stencilZFail, stencilZPass);

					currentStencilFail = stencilFail;
					currentStencilZFail = stencilZFail;
					currentStencilZPass = stencilZPass;
				}
			},

			setLocked: function (lock) {
				locked = lock;
			},

			setClear: function (stencil) {
				if (currentStencilClear !== stencil) {
					gl.clearStencil(stencil);
					currentStencilClear = stencil;
				}
			},

			reset: function () {
				locked = false;

				currentStencilMask = null;
				currentStencilFunc = null;
				currentStencilRef = null;
				currentStencilFuncMask = null;
				currentStencilFail = null;
				currentStencilZFail = null;
				currentStencilZPass = null;
				currentStencilClear = null;
			},
		};
	}

	//

	const colorBuffer = new ColorBuffer();
	const depthBuffer = new DepthBuffer();
	const stencilBuffer = new StencilBuffer();

	let enabledCapabilities = {};

	let currentBoundFramebuffers = {};
	let currentDrawbuffers = new WeakMap();
	let defaultDrawbuffers = [];

	let currentProgram = null;

	let currentBlendingEnabled = false;
	let currentBlending = null;
	let currentBlendEquation = null;
	let currentBlendSrc = null;
	let currentBlendDst = null;
	let currentBlendEquationAlpha = null;
	let currentBlendSrcAlpha = null;
	let currentBlendDstAlpha = null;
	let currentPremultipledAlpha = false;

	let currentFlipSided = null;
	let currentCullFace = null;

	let currentLineWidth = null;

	let currentPolygonOffsetFactor = null;
	let currentPolygonOffsetUnits = null;

	const maxTextures = gl.getParameter(gl.MAX_COMBINED_TEXTURE_IMAGE_UNITS);

	let lineWidthAvailable = false;
	let version = 0;
	const glVersion = gl.getParameter(gl.VERSION);

	if (glVersion.indexOf('WebGL') !== -1) {
		version = parseFloat(/^WebGL (\d)/.exec(glVersion)[1]);
		lineWidthAvailable = version >= 1.0;
	} else if (glVersion.indexOf('OpenGL ES') !== -1) {
		version = parseFloat(/^OpenGL ES (\d)/.exec(glVersion)[1]);
		lineWidthAvailable = version >= 2.0;
	}

	let currentTextureSlot = null;
	let currentBoundTextures = {};

	const scissorParam = gl.getParameter(gl.SCISSOR_BOX);
	const viewportParam = gl.getParameter(gl.VIEWPORT);

	const currentScissor = new Vector4().fromArray(scissorParam);
	const currentViewport = new Vector4().fromArray(viewportParam);

	function createTexture(type, target, count) {
		const data = new Uint8Array(4); // 4 is required to match default unpack alignment of 4.
		const texture = gl.createTexture();

		gl.bindTexture(type, texture);
		gl.texParameteri(type, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
		gl.texParameteri(type, gl.TEXTURE_MAG_FILTER, gl.NEAREST);

		for (let i = 0; i < count; i++) {
			gl.texImage2D(target + i, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, data);
		}

		return texture;
	}

	const emptyTextures = {};
	emptyTextures[gl.TEXTURE_2D] = createTexture(gl.TEXTURE_2D, gl.TEXTURE_2D, 1);
	emptyTextures[gl.TEXTURE_CUBE_MAP] = createTexture(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_CUBE_MAP_POSITIVE_X, 6);

	// init

	colorBuffer.setClear(0, 0, 0, 1);
	depthBuffer.setClear(1);
	stencilBuffer.setClear(0);

	enable(gl.DEPTH_TEST);
	depthBuffer.setFunc(LessEqualDepth);

	setFlipSided(false);
	setCullFace(CullFaceBack);
	enable(gl.CULL_FACE);

	setBlending(NoBlending);

	//

	function enable(id) {
		if (enabledCapabilities[id] !== true) {
			gl.enable(id);
			enabledCapabilities[id] = true;
		}
	}

	function disable(id) {
		if (enabledCapabilities[id] !== false) {
			gl.disable(id);
			enabledCapabilities[id] = false;
		}
	}

	function bindFramebuffer(target, framebuffer) {
		if (currentBoundFramebuffers[target] !== framebuffer) {
			gl.bindFramebuffer(target, framebuffer);

			currentBoundFramebuffers[target] = framebuffer;

			if (isWebGL2) {
				// gl.DRAW_FRAMEBUFFER is equivalent to gl.FRAMEBUFFER

				if (target === gl.DRAW_FRAMEBUFFER) {
					currentBoundFramebuffers[gl.FRAMEBUFFER] = framebuffer;
				}

				if (target === gl.FRAMEBUFFER) {
					currentBoundFramebuffers[gl.DRAW_FRAMEBUFFER] = framebuffer;
				}
			}

			return true;
		}

		return false;
	}

	function drawBuffers(renderTarget, framebuffer) {
		let drawBuffers = defaultDrawbuffers;

		let needsUpdate = false;

		if (renderTarget) {
			drawBuffers = currentDrawbuffers.get(framebuffer);

			if (drawBuffers === undefined) {
				drawBuffers = [];
				currentDrawbuffers.set(framebuffer, drawBuffers);
			}

			if (renderTarget.isWebGLMultipleRenderTargets) {
				const textures = renderTarget.texture;

				if (drawBuffers.length !== textures.length || drawBuffers[0] !== gl.COLOR_ATTACHMENT0) {
					for (let i = 0, il = textures.length; i < il; i++) {
						drawBuffers[i] = gl.COLOR_ATTACHMENT0 + i;
					}

					drawBuffers.length = textures.length;

					needsUpdate = true;
				}
			} else {
				if (drawBuffers[0] !== gl.COLOR_ATTACHMENT0) {
					drawBuffers[0] = gl.COLOR_ATTACHMENT0;

					needsUpdate = true;
				}
			}
		} else {
			if (drawBuffers[0] !== gl.BACK) {
				drawBuffers[0] = gl.BACK;

				needsUpdate = true;
			}
		}

		if (needsUpdate) {
			if (capabilities.isWebGL2) {
				gl.drawBuffers(drawBuffers);
			} else {
				extensions.get('WEBGL_draw_buffers').drawBuffersWEBGL(drawBuffers);
			}
		}
	}

	function useProgram(program) {
		if (currentProgram !== program) {
			gl.useProgram(program);

			currentProgram = program;

			return true;
		}

		return false;
	}

	const equationToGL = {
		[AddEquation]: gl.FUNC_ADD,
		[SubtractEquation]: gl.FUNC_SUBTRACT,
		[ReverseSubtractEquation]: gl.FUNC_REVERSE_SUBTRACT,
	};

	if (isWebGL2) {
		equationToGL[MinEquation] = gl.MIN;
		equationToGL[MaxEquation] = gl.MAX;
	} else {
		const extension = extensions.get('EXT_blend_minmax');

		if (extension !== null) {
			equationToGL[MinEquation] = extension.MIN_EXT;
			equationToGL[MaxEquation] = extension.MAX_EXT;
		}
	}

	const factorToGL = {
		[ZeroFactor]: gl.ZERO,
		[OneFactor]: gl.ONE,
		[SrcColorFactor]: gl.SRC_COLOR,
		[SrcAlphaFactor]: gl.SRC_ALPHA,
		[SrcAlphaSaturateFactor]: gl.SRC_ALPHA_SATURATE,
		[DstColorFactor]: gl.DST_COLOR,
		[DstAlphaFactor]: gl.DST_ALPHA,
		[OneMinusSrcColorFactor]: gl.ONE_MINUS_SRC_COLOR,
		[OneMinusSrcAlphaFactor]: gl.ONE_MINUS_SRC_ALPHA,
		[OneMinusDstColorFactor]: gl.ONE_MINUS_DST_COLOR,
		[OneMinusDstAlphaFactor]: gl.ONE_MINUS_DST_ALPHA,
	};

	function setBlending(blending, blendEquation, blendSrc, blendDst, blendEquationAlpha, blendSrcAlpha, blendDstAlpha, premultipliedAlpha) {
		if (blending === NoBlending) {
			if (currentBlendingEnabled === true) {
				disable(gl.BLEND);
				currentBlendingEnabled = false;
			}

			return;
		}

		if (currentBlendingEnabled === false) {
			enable(gl.BLEND);
			currentBlendingEnabled = true;
		}

		if (blending !== CustomBlending) {
			if (blending !== currentBlending || premultipliedAlpha !== currentPremultipledAlpha) {
				if (currentBlendEquation !== AddEquation || currentBlendEquationAlpha !== AddEquation) {
					gl.blendEquation(gl.FUNC_ADD);

					currentBlendEquation = AddEquation;
					currentBlendEquationAlpha = AddEquation;
				}

				if (premultipliedAlpha) {
					switch (blending) {
						case NormalBlending:
							gl.blendFuncSeparate(gl.ONE, gl.ONE_MINUS_SRC_ALPHA, gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
							break;

						case AdditiveBlending:
							gl.blendFunc(gl.ONE, gl.ONE);
							break;

						case SubtractiveBlending:
							gl.blendFuncSeparate(gl.ZERO, gl.ZERO, gl.ONE_MINUS_SRC_COLOR, gl.ONE_MINUS_SRC_ALPHA);
							break;

						case MultiplyBlending:
							gl.blendFuncSeparate(gl.ZERO, gl.SRC_COLOR, gl.ZERO, gl.SRC_ALPHA);
							break;

						default:
							console.error('THREE.WebGLState: Invalid blending: ', blending);
							break;
					}
				} else {
					switch (blending) {
						case NormalBlending:
							gl.blendFuncSeparate(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA, gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
							break;

						case AdditiveBlending:
							gl.blendFunc(gl.SRC_ALPHA, gl.ONE);
							break;

						case SubtractiveBlending:
							gl.blendFunc(gl.ZERO, gl.ONE_MINUS_SRC_COLOR);
							break;

						case MultiplyBlending:
							gl.blendFunc(gl.ZERO, gl.SRC_COLOR);
							break;

						default:
							console.error('THREE.WebGLState: Invalid blending: ', blending);
							break;
					}
				}

				currentBlendSrc = null;
				currentBlendDst = null;
				currentBlendSrcAlpha = null;
				currentBlendDstAlpha = null;

				currentBlending = blending;
				currentPremultipledAlpha = premultipliedAlpha;
			}

			return;
		}

		// custom blending

		blendEquationAlpha = blendEquationAlpha || blendEquation;
		blendSrcAlpha = blendSrcAlpha || blendSrc;
		blendDstAlpha = blendDstAlpha || blendDst;

		if (blendEquation !== currentBlendEquation || blendEquationAlpha !== currentBlendEquationAlpha) {
			gl.blendEquationSeparate(equationToGL[blendEquation], equationToGL[blendEquationAlpha]);

			currentBlendEquation = blendEquation;
			currentBlendEquationAlpha = blendEquationAlpha;
		}

		if (blendSrc !== currentBlendSrc || blendDst !== currentBlendDst || blendSrcAlpha !== currentBlendSrcAlpha || blendDstAlpha !== currentBlendDstAlpha) {
			gl.blendFuncSeparate(factorToGL[blendSrc], factorToGL[blendDst], factorToGL[blendSrcAlpha], factorToGL[blendDstAlpha]);

			currentBlendSrc = blendSrc;
			currentBlendDst = blendDst;
			currentBlendSrcAlpha = blendSrcAlpha;
			currentBlendDstAlpha = blendDstAlpha;
		}

		currentBlending = blending;
		currentPremultipledAlpha = null;
	}

	function setMaterial(material, frontFaceCW) {
		material.side === DoubleSide ? disable(gl.CULL_FACE) : enable(gl.CULL_FACE);

		let flipSided = material.side === BackSide;
		if (frontFaceCW) flipSided = !flipSided;

		setFlipSided(flipSided);

		material.blending === NormalBlending && material.transparent === false
			? setBlending(NoBlending)
			: setBlending(
					material.blending,
					material.blendEquation,
					material.blendSrc,
					material.blendDst,
					material.blendEquationAlpha,
					material.blendSrcAlpha,
					material.blendDstAlpha,
					material.premultipliedAlpha
			  );

		depthBuffer.setFunc(material.depthFunc);
		depthBuffer.setTest(material.depthTest);
		depthBuffer.setMask(material.depthWrite);
		colorBuffer.setMask(material.colorWrite);

		const stencilWrite = material.stencilWrite;
		stencilBuffer.setTest(stencilWrite);
		if (stencilWrite) {
			stencilBuffer.setMask(material.stencilWriteMask);
			stencilBuffer.setFunc(material.stencilFunc, material.stencilRef, material.stencilFuncMask);
			stencilBuffer.setOp(material.stencilFail, material.stencilZFail, material.stencilZPass);
		}

		setPolygonOffset(material.polygonOffset, material.polygonOffsetFactor, material.polygonOffsetUnits);

		material.alphaToCoverage === true ? enable(gl.SAMPLE_ALPHA_TO_COVERAGE) : disable(gl.SAMPLE_ALPHA_TO_COVERAGE);
	}

	//

	function setFlipSided(flipSided) {
		if (currentFlipSided !== flipSided) {
			if (flipSided) {
				gl.frontFace(gl.CW);
			} else {
				gl.frontFace(gl.CCW);
			}

			currentFlipSided = flipSided;
		}
	}

	function setCullFace(cullFace) {
		if (cullFace !== CullFaceNone) {
			enable(gl.CULL_FACE);

			if (cullFace !== currentCullFace) {
				if (cullFace === CullFaceBack) {
					gl.cullFace(gl.BACK);
				} else if (cullFace === CullFaceFront) {
					gl.cullFace(gl.FRONT);
				} else {
					gl.cullFace(gl.FRONT_AND_BACK);
				}
			}
		} else {
			disable(gl.CULL_FACE);
		}

		currentCullFace = cullFace;
	}

	function setLineWidth(width) {
		if (width !== currentLineWidth) {
			if (lineWidthAvailable) gl.lineWidth(width);

			currentLineWidth = width;
		}
	}

	function setPolygonOffset(polygonOffset, factor, units) {
		if (polygonOffset) {
			enable(gl.POLYGON_OFFSET_FILL);

			if (currentPolygonOffsetFactor !== factor || currentPolygonOffsetUnits !== units) {
				gl.polygonOffset(factor, units);

				currentPolygonOffsetFactor = factor;
				currentPolygonOffsetUnits = units;
			}
		} else {
			disable(gl.POLYGON_OFFSET_FILL);
		}
	}

	function setScissorTest(scissorTest) {
		if (scissorTest) {
			enable(gl.SCISSOR_TEST);
		} else {
			disable(gl.SCISSOR_TEST);
		}
	}

	// texture

	function activeTexture(webglSlot) {
		if (webglSlot === undefined) webglSlot = gl.TEXTURE0 + maxTextures - 1;

		if (currentTextureSlot !== webglSlot) {
			gl.activeTexture(webglSlot);
			currentTextureSlot = webglSlot;
		}
	}

	function bindTexture(webglType, webglTexture) {
		if (currentTextureSlot === null) {
			activeTexture();
		}

		let boundTexture = currentBoundTextures[currentTextureSlot];

		if (boundTexture === undefined) {
			boundTexture = { type: undefined, texture: undefined };
			currentBoundTextures[currentTextureSlot] = boundTexture;
		}

		if (boundTexture.type !== webglType || boundTexture.texture !== webglTexture) {
			gl.bindTexture(webglType, webglTexture || emptyTextures[webglType]);

			boundTexture.type = webglType;
			boundTexture.texture = webglTexture;
		}
	}

	function unbindTexture() {
		const boundTexture = currentBoundTextures[currentTextureSlot];

		if (boundTexture !== undefined && boundTexture.type !== undefined) {
			gl.bindTexture(boundTexture.type, null);

			boundTexture.type = undefined;
			boundTexture.texture = undefined;
		}
	}

	function compressedTexImage2D() {
		try {
			gl.compressedTexImage2D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texSubImage2D() {
		try {
			gl.texSubImage2D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texSubImage3D() {
		try {
			gl.texSubImage3D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function compressedTexSubImage2D() {
		try {
			gl.compressedTexSubImage2D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texStorage2D() {
		try {
			gl.texStorage2D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texStorage3D() {
		try {
			gl.texStorage3D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texImage2D() {
		try {
			gl.texImage2D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	function texImage3D() {
		try {
			gl.texImage3D.apply(gl, arguments);
		} catch (error) {
			console.error('THREE.WebGLState:', error);
		}
	}

	//

	function scissor(scissor) {
		if (currentScissor.equals(scissor) === false) {
			gl.scissor(scissor.x, scissor.y, scissor.z, scissor.w);
			currentScissor.copy(scissor);
		}
	}

	function viewport(viewport) {
		if (currentViewport.equals(viewport) === false) {
			gl.viewport(viewport.x, viewport.y, viewport.z, viewport.w);
			currentViewport.copy(viewport);
		}
	}

	//

	function reset() {
		// reset state

		gl.disable(gl.BLEND);
		gl.disable(gl.CULL_FACE);
		gl.disable(gl.DEPTH_TEST);
		gl.disable(gl.POLYGON_OFFSET_FILL);
		gl.disable(gl.SCISSOR_TEST);
		gl.disable(gl.STENCIL_TEST);
		gl.disable(gl.SAMPLE_ALPHA_TO_COVERAGE);

		gl.blendEquation(gl.FUNC_ADD);
		gl.blendFunc(gl.ONE, gl.ZERO);
		gl.blendFuncSeparate(gl.ONE, gl.ZERO, gl.ONE, gl.ZERO);

		gl.colorMask(true, true, true, true);
		gl.clearColor(0, 0, 0, 0);

		gl.depthMask(true);
		gl.depthFunc(gl.LESS);
		gl.clearDepth(1);

		gl.stencilMask(0xffffffff);
		gl.stencilFunc(gl.ALWAYS, 0, 0xffffffff);
		gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
		gl.clearStencil(0);

		gl.cullFace(gl.BACK);
		gl.frontFace(gl.CCW);

		gl.polygonOffset(0, 0);

		gl.activeTexture(gl.TEXTURE0);

		gl.bindFramebuffer(gl.FRAMEBUFFER, null);

		if (isWebGL2 === true) {
			gl.bindFramebuffer(gl.DRAW_FRAMEBUFFER, null);
			gl.bindFramebuffer(gl.READ_FRAMEBUFFER, null);
		}

		gl.useProgram(null);

		gl.lineWidth(1);

		gl.scissor(0, 0, gl.canvas.width, gl.canvas.height);
		gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

		// reset internals

		enabledCapabilities = {};

		currentTextureSlot = null;
		currentBoundTextures = {};

		currentBoundFramebuffers = {};
		currentDrawbuffers = new WeakMap();
		defaultDrawbuffers = [];

		currentProgram = null;

		currentBlendingEnabled = false;
		currentBlending = null;
		currentBlendEquation = null;
		currentBlendSrc = null;
		currentBlendDst = null;
		currentBlendEquationAlpha = null;
		currentBlendSrcAlpha = null;
		currentBlendDstAlpha = null;
		currentPremultipledAlpha = false;

		currentFlipSided = null;
		currentCullFace = null;

		currentLineWidth = null;

		currentPolygonOffsetFactor = null;
		currentPolygonOffsetUnits = null;

		currentScissor.set(0, 0, gl.canvas.width, gl.canvas.height);
		currentViewport.set(0, 0, gl.canvas.width, gl.canvas.height);

		colorBuffer.reset();
		depthBuffer.reset();
		stencilBuffer.reset();
	}

	return {
		buffers: {
			color: colorBuffer,
			depth: depthBuffer,
			stencil: stencilBuffer,
		},

		enable: enable,
		disable: disable,

		bindFramebuffer: bindFramebuffer,
		drawBuffers: drawBuffers,

		useProgram: useProgram,

		setBlending: setBlending,
		setMaterial: setMaterial,

		setFlipSided: setFlipSided,
		setCullFace: setCullFace,

		setLineWidth: setLineWidth,
		setPolygonOffset: setPolygonOffset,

		setScissorTest: setScissorTest,

		activeTexture: activeTexture,
		bindTexture: bindTexture,
		unbindTexture: unbindTexture,
		compressedTexImage2D: compressedTexImage2D,
		texImage2D: texImage2D,
		texImage3D: texImage3D,

		texStorage2D: texStorage2D,
		texStorage3D: texStorage3D,
		texSubImage2D: texSubImage2D,
		texSubImage3D: texSubImage3D,
		compressedTexSubImage2D: compressedTexSubImage2D,

		scissor: scissor,
		viewport: viewport,

		reset: reset,
	};
}

export { WebGLState };